1. Field of the Invention
This invention relates to a truck and, more particulary, to a truck for a railway vehicle with a truck frame and four rotatable wheels where one pair of the wheels are driven.
2. Description of the Prior Art
A truck of this type disclosed in DE 38 08 593 that is used in particular for low-floor streetcars, has a truck frame and four individual wheels, i.e. 2 pairs of wheels, each of which is mounted so that it can rotate around horizontal axles on a hub carrier that is mounted on the truck frame so that it can pivot around a horizontal axis. The hub carriers are thereby fastened by flanges on the free ends of longitudinal beams of the truck frame, whereby next to each individual wheel there is a primary spring which is inserted between the hub carrier and the longitudinal beam located above it. The axles of the individual wheels are rigidly connected with the respective hub carriers. One wheel set on the same axle is thereby driven, for which purpose each individual wheel in question is coupled with a transmission. The two transmissions are jointly driven by a drive motor via a coupler mechanism.
The object of the invention is to create a truck which can travel with minimal wear, maximum safety and low construction costs in both tight curves and, at higher speeds, in straight portions of the track.
In one configuration of a truck as claimed by the invention, the non-driven wheels, which are generally the leading wheels in the direction of travel of the railway vehicle, can be adjusted automatically radially with respect to the rail and in particular to the curved rail, on account of their mounting that allows each of them to pivot around a vertical axis, and their ability to rotate freely on account of the wheel-rail geometry, whereby the steering device that is associated with this wheel pair forces the synchronized steering of both wheels. The non-driven wheels of the leading wheel set, which is constructed of a self-regulating single wheel module, as a result of their ability to pivot with respect to the joint hub carrier, can equalize the oscillations that occur at higher speeds, without transmitting the resulting movements in their full magnitude to the truck frame, which for its part supports the associated car body by means of primary springs. In addition, however, the other, driven wheel pair is mounted so that it can pivot around a vertical axis-which in this case is a common vertical axis-with respect to the truck frame. The pivoting of the driven wheel pair is thereby accomplished by means of an actively controlled actuator which, as a function of the radius of the current segment of track over which the train is traveling, determines the pivoting angle of this wheel pair, whereby its pivoting angle is opposite to the pivoting direction of the non-driven wheel pair. The pivoting occurs so that the wheel axes are oriented radially with respect to the track segment being traveled and the wheel planes are oriented tangentially to the track. The common hub carrier is thereby coupled to the truck frame so that it can pivot around a horizontal axis, and on the other hand is supported by means of primary springs against the underside of the truck frame. The individual wheels of the non-driven wheel pair, on the other hand, are preferably each mounted on individual hub carriers, which for their part are also mounted on a common hub carrier that is held on the truck frame so that it can pivot around a horizontal axis, so that the individual wheels can each be pivoted around a vertical axis. This hub carrier is also supported by means of primary springs against the underside of the truck frame, to provide the necessary ride comfort.
To achieve a defined ride of a truck as claimed by the invention, even if the operational control means to steer the driven wheel pair fail, a controllable reset device is associated with at least one wheel pair, and in this case preferably with the driven wheel pair. This reset device is optionally active if a control error is recorded. In that case, the operational steering control is deactivated, and instead the reset device is activated and automatically pivots the wheel pair or pairs, regardless of the radius of the track segment currently over which the vehicle is traveling, into a base position that is associated with a straight track. Preferably, in that case, a deceleration or braking process is also requested or automatically initiated to reduce the speed of the vehicle, if the speed is greater than a predetermined value and the radius of the curve is below a predetermined value. The allowable speed can thereby be controlled as a function of the radius of curvature of the track. But even in normal operation it is appropriate to lock the steerable hub carriers in the straight-ahead position by means of a blocking device which is preferably associated with the reset device if the radius of curvature assumes radius values that are above a predetermined threshold. The steering is thereby relieved of traction forces and the effects of abnormalities in the positions of the rails.
To minimize the steering action and thus maximize the ride comfort and to simultaneously achieve low wear between the wheels and the track, the actuator of the driven wheel set is appropriately set at the diametrically opposite angle as a function of the steering angle of at least one of the non-driven, forward individual wheels. Wear and noise generation are thereby reduced to minimum values, in particular when the vehicle is entering a curve from a straight track, or exiting a curve to a straight track, or is entering a transition curve from a straight track or exiting a transition curve into a straight track.
The steering device for the non-driven rail wheels is preferably equipped with a steering linkage which, together with the corresponding common hub carrier, forms a parallelogram suspension. The individual wheels which turn on their own thereby form a wheel set which is automatically oriented radially as a function of the forces that result from the wheel-rail geometry with regard to the track on which the vehicle is currently traveling. This advantageous effect is thereby also achieved in a track curve with a constant radius.
Between the steering linkage and the corresponding hub carriers or the truck frame, a damper or shock absorber can be inserted with a regulated suspension and damping action. The effects of uneven tracks and similar conditions are thereby not transmitted in their full magnitude into the control action of the non-driven wheels. The damping action can thereby be controlled as a function of the track curvature, and can assume very high values on the straight track. The above-mentioned blocking can also be thereby controlled. The shock absorber can accordingly be simultaneously constructed in the form of a blocking device, which suppresses adverse effects on the steering action not only in the straight track but also on a curve with a constant radius. It is thereby also appropriate to associate a displacement measurement device with at least one shock absorber and/or one actuator that corresponds to the driven wheels or even the independent reset device, if any, whereby the changes in the length of the displacement device can be used to measure the current steering angle of the individual wheels or wheel pairs to which it is coupled.
It is also possible, instead of a mechanical steering linkage, to provide a hydraulic coupling for the synchronous steering of the non-driven wheels, which forces the individual wheels to rotate by the same angle around their vertical axis.
In an articulated railway vehicle that has only one truck located in the longitudinal center of each car body, it is appropriate to arrange the trucks so that on vehicles that travel in only one direction, all of the non-driven wheel pairs are in front of the driven wheel pairs of the corresponding truck. On articulated railway vehicles that operate in two directions, on the other hand, the trucks are arranged so that the non-driven wheel pairs of the trucks in the end positions are toward the neighboring free ends of the vehicle with respect to the corresponding driven wheel pair. On the trucks located in between, the arrangement should be made, as far as possible, so that one driven wheel set is followed by another driven wheel set of the neighboring truck.